This invention relates to DC contactors for electrical systems.
Generally available high voltage DC contactors, for operation at voltage levels up to at least about 300 volts are electromechanical devices that use mechanical blowout mechanisms for extinguishing the arc that results from opening the contacts. Arc extinction can be particularly important when interrupting current flow to inductive loads, or resistive loads where the conductive leads themselves provide substantial inductance. The blowout mechanisms are inherently large, heavy, and slow and entail a relatively long arcing time upon opening.
High voltage DC power systems are of present interest for use in aircraft because of improved distribution efficiency and elimination of the constant speed drive required for 400 Hz systems, as have been conventional. In applications such as aircraft systems, size and weight are of extreme importance and load transients and power dissipation must be minimized.
It is possible to avoid arcing altogether by making DC contactors utilizing solid state components, for example transistors, as the switching elements in avoiding the use of any mechanical contacts. At present, however, such DC contactors are considered feasible only at modest current levels, such as less than about 50 amperes. When higher steady state currents are encountered, the power dissipation and heating in the solid state componets gets quite large. On the other hand, electromechanical relays offer the advantage of providing high current switching with minimum dissipation in the steady state, that is, when the relay is on and the contacts are closed.
The present invention seeks the objectives of a DC contactor with high current and voltage handling capability where arc quenching is rapid and achievable by minimal size and weight components.
In part, the objectives of this invention have been addressed by the prior art. For example, U.S. Pat. No. 3,309,570, Mar. 14, 1967, is directed to an arcless interruper wherein an electromechanical contactor is provided with a circuit for diverting current away from the contacts upon opening and imposing a reverse voltage across the contacts. Such apparatus is intended to avoid creation of any arc, not to rapidly quench an arc upon its initiation. Such apparatus of the prior art has characteristics impairing performance. Speed of operation, bi-directional capability, and avoidance of substantial voltage transients to the load are among the qualities desirably improved.